Multilayered glass laminate having enhanced resistance to penetration by high velocity projectiles

ABSTRACT

A multilayered glass laminate having enhanced resistance to spalling and penetration by high velocity projectiles consists of at least three plies of glass (10, 12, 14) with layers of plasticized polyvinyl butyral (16, 18, 20) therebetween and having permanently bonded to an outer layer of one of said plies of glass (14) a thin composite consisting of an adhesive energy absorbing layer (22) and a dimensionally stable polyester film (24).

BACKGROUND OF THE INVENTION

This invention relates to glass laminates having enhanced resistance topenetration by high velocity projectiles. More particularly, theinvention relates to relatively thin glass laminates which not only stopglass from spalling when impacted by small and medium caliber bulletsbut also stops penetration of the laminates by the bullets or othersmall high velocity projectiles.

Various types of transparent laminated structures have been disclosedfor protecting personnel from flying splinters and fragments of glazingmaterials which are released when a high velocity projectile strikes thestructure. In U.S. Pat. No. 3,658,636 thick plates of an amorphouspolyamide are formed into a sandwich structure with silicate glass. U.S.Pat. No. 2,861,021 describes a structure in which polymethylmethacrylate sheets are laminated with polyvinyl butyral and faced witha layer of a polyamide, polyester or regenerated cellulose sheet.Multiple plies of glass and polyvinyl butyral are used in combinationwith a plastic interlayer as an impact absorption section in thestructure disclosed in U.S. Pat. No. 4,130,684.

The problem of spalling of an anti-abrasion layer which is applied to alaminate using polycarbonate sheets is addressed in U.S. Pat. No.4,812,359 by applying a thin polycarbonate sheet having anabrasion-resistant self-healing coating. A similar laminate whichincludes an internal elastic expansion core with a thin polycarbonatesheet covered with an antiabrasive which can be replaced is disclosed inU.S. Pat. No. 4,879,183. British Patent 828,381 discloses a five layerlaminate consisting of two layers of glass, two layers of polyvinylbutyrate and a central layer of polyethylene terephthalate. Published UKApplication 2 156 736A discloses an impact resistant laminate comprisinga number of glass sheets which are laminated together with a rearpolycarbonate sheet which is said to be resistant to spalling.

A problem with most "bullet resistant" structures is that they have athickness in excess of that which can be accommodated in usual glazingapplications. Some structures are effective in controlling spalling butare not effective in stopping penetration of the laminate by aprojectile. Most of the structures rely on incorporating layers ofvarious materials in the laminated structure. This complicatesmanufacture and increases costs since different materials requiredifferent laminating techniques.

It has been found that by permanently bonding a very thin compositeconsisting of an adhesive layer and a dimensionally stable polyesterfilm to multiple plies of glass with layers of plasticized polyvinylbutyral there between, a glass laminate of substantially reducedthickness is provided which is capable of resisting penetration of highvelocity projectiles with little, if any, spalling from the inner rearface of the laminate.

SUMMARY OF THE INVENTION

This invention provides a laminated glazing to which is attached apermanent, energy absorbing thin plastic composite consisting of anadhesive energy absorbing layer, such as polyvinyl butyral, and astrong, dimensionally stable, chemical and abrasion resistant layer,such as a layer of polyester film which may be coated with apolysiloxane or other abrasion resistant coating. The thin plasticcomposite prevents spalling from the surface of the glazing to which ithas been laminated. Surprisingly, in addition to stopping glass fromspalling, the composite increases the integrity and penetrationresistance of the constructions to which it is laminated when they areimpacted by bullets or other projectiles striking the opposite surface.By retaining the surface glass and holding the construction together,and by other mechanisms not fully understood, penetration resistance issubstantially enhanced far beyond what would be expected of such a thincomposite structure.

In accordance with this invention a multilayered glass laminateconsisting of at least three plies of glass is prepared by interposinglayers of plasticized polyvinyl butyral between the plies of glass. Theplies of glass each should have a thickness from about 1/8 to about 1/4inch (3.175 to 6.35 mm) and the polyvinyl butyral layer should have athickness from about 15 to about 60 mils (0.381 to 1.524 mm). A thincomposite consisting of an adhesive layer of polyvinyl butyral having athickness from 15 to 60 mils (0.381 to 1.524 mm) and a polyester filmhaving a thickness from about 3 to about 15 mils (0.0762 to 0.381 mm) ispermanently bonded to an outer layer of the glass. The total thicknessof the composite is not greater than about 2 mm; Anti-spalling andpenetration resistant structures having an overall reduction inthickness of 20% or more as compared to known glass laminates used inbullet resistant glazing applications are provided by this invention.Preferably, three to seven plies of glass adhered together with adhesivelayers of polyvinyl butyral are used. It is to be understood that therelative thickness and number of plies of glass of the structures ofthis invention will be determined by the "threat level", i.e. the sizeand velocity of projectiles which are expected to be encountered.

The polyvinyl butyral adhesive sheeting my be selected from the manycommercially available grades of plasticized polyvinyl butyral. Aparticularly desirable product of the type disclosed in Moynihan, U.S.Pat. No. 4,292,372 is sold by E. I. Du Pont de Nemours and Company underthe trademark Butacite®. Other known adhesive material for glasslaminates such as polyurethane my also be used. The polyester film maybe of the type disclosed in Knox, U.S. Pat. No. 4,072,779, and may becoated with an abrasion resistant material as disclosed in that patent.The glass may be selected in accordance with ASTM specifications,Desigrmdon C 1172-91. The glass may be tempered or annealed. Temperedglass is generally preferred.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are sections through the edge of a projectile resistantlaminate according to the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a projectile resistant laminate comprises threesheets 10, 12, and 14 of glass. Glass sheet 10 is positioned in adirection likely to receive an impact from a projectile, e.g. a bullet,on its face 11. Sheets 10, 12, and 14 are bonded together by interlayersof polyvinyl butyral which are from 15 to 60 mils (0.381 to 1.528 mm)thick. A polyethylene terephthalate film 24 from 3 to 15 mils (0.0762 to0.381 mm) thick is bonded to glass sheet 14 by an interlayer ofpolyvinyl butyral.

FIG. 2 shows the laminate of FIG. 1 having an abrasion resistant coating26 adhered to the outer surface of polyethylene terephthalate film 24.Coating 26 may be a silanol coating from 1 to 20 microns thick of thetype disclosed in U.S. Pat. No. 4,469,743 and U.S. Pat. No. 4,177,315.

The laminated structure of this invention may be prepared by knownlaminating methods. Polyvinyl butyral film is interleaved between glasssheets 10, 12 and 14. A composite comprised of polyethyleneterephthalate film 24 and polyvinyl butyral film 22 is then positionedover the rear face of glass sheet 14. A coverplate is placed over theassembly, the assembly is edge taped and placed in an airtight bag andsubjected to a vacuum. The evacuated assembly is then autoclaved whilethe bag is maintained under reduced pressure.

The invention will be further illustrated by the following examples.

EXAMPLES

Laminated glass test panels were prepared by sandwiching polyvinylbutyral sheeting having a thickness of 30 mils (0.762 mm) between onefoot (304.8 mm)squares of nominal 100 mil (2.54 mm) thick glass.Selected panels included a composite bonded to an outer layer of one ofthe plies of glass consisting of a layer of a Butacite® polyvinylbutyral sheet having a thickness of 15 mils (0.381 mm) and a polyesterfilm having a thickness of 0.007 inch (0.178 m). A Single shot from a0.38 caliber handgun was fired at the center of each panel from adistance of 15 feet (4.572 m). Spall was measured as grams of glassejecting from the backside of the laminate. Spall designated "+++" wasnot measured but was estimated to be in the range from about 50 to 100grams, designated "++" in the range from 10 to 15 grams, and "+" lessthan about 0.2 grams. The results of the tests are set out in thefollowing table.

                                      TABLE 1                                     __________________________________________________________________________    STANDARD GLASS                                                                LAMINATE                  COMPOSITE GLASS LAMINATE                            NO. OF                                                                             THICKNESS       SPALL                                                                              THICKNESS       SPALL                               PLIES                                                                              (mm)    PENETRATE                                                                             (gm) (mm)    PENETRATE                                                                             (gm)                                __________________________________________________________________________    4    11.94   YES     85.1 12.45   NO      0.0                                 4                         12.95   NO      0.0                                 4                         12.45   NO      0.0                                 4                         12.45   YES     +++                                 5    15.24   NO      10.3 15.75   NO      0.0                                 5    15.24   NO      ++   15.49   NO      0.0                                 5    15.24   YES     +++  15.49   NO      0.0                                 5    15      NO      +++  15.75   NO      0.0                                 5    15      YES     +++                                                      6    18.3    NO      13.7                                                     6    18      NO      ++                                                       7    21.34   NO      9.5                                                      7    21.34   NO      0.0                                                      7    21.84   NO      ++                                                       8    24.38   NO      0.29                                                     9    27.94   NO      +                                                        __________________________________________________________________________

Results similar to those obtained with 4 plies of glass plus a compositeas shown above are obtained using 3 plies of glass plus a compositehaving a total thickness of about 12.5 mm.

In Table 2 the data from Table 1 is condensed and reformated to show apercentage of penetration versus sample construction, thickness and theratio of penetrations to the number of samples tested for each type.Focusing on the samples each with 4 plies of glass, the standardlaminate was penetrated, whereas the sample having the same number ofplies plus the composite shield is only penetrated 25% of the time. Intests where the composite was not penetrated, no spall was generated.This improvement resulted from the addition of a polyethyleneterephthalate and polyvinyl butyral adhesive film of only 22 mils (0.559mm) thick as compared to a glass laminate thickness of about 0.5 inch(12.7 mm) (an increase of 6.4% in thickness). The same pattern can beseen for the samples each containing 5 plies of glass, where the numberof data sets is greater. In this case, the addition of the compositereduces the penetration frequency from 40% to 0% with an increase ofonly 33% in thickness. It is obvious when comparing 5 plies of StandardGlass Laminate that more protection is afforded when 4 plies of the samethickness of glass is used in the Composite Glass Laminate of thepresent invention. Even increasing the laminate thickness to 0.6 inch(1524 mm), (5 plies of laminated glass) only reduced the actualpenetration to 40% (a 27.7% increase in thickness). To obtain 0%penetration with the standard construction, 6 plies of glass werenecessary.

                                      TABLE 2                                     __________________________________________________________________________    STANDARD GLASS                                                                LAMINATE                 COMPOSITE GLASS LAMINATE                             NO. THKNSS                                                                              PENE-     SPALL                                                                              THKNSS                                                                              PENE-     SPALL                                PLIES                                                                             (mm)  TRATE                                                                              RATIO                                                                              (gm) (mm)  TRATE                                                                              RATIO                                                                              (gm)                                 __________________________________________________________________________    4   11.94 100% 1/1  85.1 12.7  25%  1/4  0.0                                  5   15.24 40%  2/5  10.3 15.62  0%  0/4  0.0                                  6   18.3  0%   0/2  13.7                                                      7   21.59 0%   0/3  9.5                                                       8   24.38 0%   0/1  0.2                                                       9   27.94 0%   0/1  +                                                         11  35.56 0%   0/1  0.0                                                       __________________________________________________________________________

I claim:
 1. A multilayered glass laminate having enhanced resistance tospalling and penetration by high velocity projectiles consisting of fromthree to seven plies of glass, each ply having a thickness from 3.175 to635 mm, with layers of plasticized polyvinyl butyral resin therebetween,said laminate having permanently bonded to an outer layer of one of saidplies of glass a thin composite consisting of an adhesive, energyabsorbing layer and a dimensionally stable, chemical resistant polyesterfilm, said composite having a thickness not greater than about 2 mm:said polyester film having a thickness of from about 0.762 to 0.381 mmand said adhesive layer having a thickness from about 0.381 to 1.524 mm.2. The laminate of claim 1 wherein said adhesive layer is plasticizedpolyvinyl butyral.
 3. The laminate of claim 2 wherein said polyesterfilm is coated with an abrasion resistant coating.